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FirefoxWeb browser · Mozilla

CVE-2026-2761

CRITICAL · 10.0 CVSS v3.1 Published 2026-02-24
Fix available
A fix is available. Upgrade to 115.33.0 / 140.8.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Sandbox escape in the Graphics: WebRender component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

A sandbox escape vulnerability exists in Mozilla's WebRender graphics component, allowing an attacker to break out of the sandbox isolation and potentially execute code outside the protected environment. This is a critical security flaw as sandbox escapes enable further system compromise beyond the initial attack vector.

MitigationApply the vendor-supplied updates: upgrade to Firefox 148, Firefox ESR 115.33/140.8, or Thunderbird 140.8 as appropriate for your deployment. Prioritize systems running affected versions exposed to untrusted content.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FirefoxWeb browser
Affected:< 115.33.0< 148.0>= 128.0, < 140.8.0
ThunderbirdApplication
Affected:< 140.8.0< 148.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed Firefox version
    Open Firefox, go to Help > About Firefox, or enter 'about:support' in the address bar and look at the 'Version' field
    Affected if Version is below 115.33.0, or between 128.0 and 140.8.0 (exclusive), or below 148.0 if not covered by the previous ranges
  2. Check installed Thunderbird version
    Open Thunderbird, go to Help > About Thunderbird, or enter 'about:support' in the address bar and look at the 'Version' field
    Affected if Version is below 140.8.0 or below 148.0
  3. Verify WebRender is enabled
    Enter 'about:support' in the Firefox or Thunderbird address bar and look for 'GPU Process' or 'WebRender' in the Graphics section; alternatively, check for 'gfx.webrender.enabled' in about:config
    Affected if WebRender is enabled (the vulnerability requires WebRender to be active in the graphics processing pipeline)

You are affected if you run a vulnerable version of Firefox or Thunderbird AND have WebRender enabled in your graphics settings.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 115.33.0 / 140.8.0 / 148.0 or later
Fixed in 115.33.0140.8.0148.0
Interim mitigation

Apply the vendor-supplied updates: upgrade to Firefox 148, Firefox ESR 115.33/140.8, or Thunderbird 140.8 as appropriate for your deployment. Prioritize systems running affected versions exposed to untrusted content.

Recommended fix High confidence

Firefox 148.0 (standard), Firefox ESR 115.33.0 (ESR 115), Firefox ESR 140.8.0 (ESR 140), Thunderbird 140.8.0, or Thunderbird 148.0

  1. 1. Identify the current installed version of Firefox or Thunderbird by checking Help > About [Product Name]
  2. 2. If running Firefox: Determine if using the standard release channel or Firefox ESR (Extended Support Release) by checking the version number
  3. 3. For Firefox standard release users: Upgrade to Firefox 148.0 or later from https://www.mozilla.org/firefox/
  4. 4. For Firefox ESR users: Determine which ESR branch is in use (115.x or 140.x) and upgrade to the corresponding fixed version: Firefox ESR 115.33.0 or Firefox ESR 140.8.0
  5. 5. For Thunderbird users: Upgrade to Thunderbird 140.8.0 or Thunderbird 148.0 from https://www.thunderbird.net/
  6. 6. Restart the application after upgrade
  7. 7. Verify the installed version matches or exceeds the fixed version by checking Help > About
Caveat Upgrades within same major version should have minimal breaking changes; however, always review release notes for potential impacts to extensions or configurations

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-2761 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data